Montana GOP Senate candidate Matt Rosendale knew in advance the National Rifle Association was poised to drop big bucks on an advertising purchase against his opponent this November.

Chris Cox, the NRA’s chief political strategist for its legislative campaign political action committee, told Rosendale the group would be “in this race,” according to audio from a July event in Washington, D.C., reported by the Daily Beast.

“Have outside groups started spending on your behalf?” a man at the event asks Rosendale in the recording.

“I fully expect the NRA is going to come in … in August sometime,” Rosendale says.

“This is a big race for the NRA,” the man says.

“Yeah. The Supreme Court confirmations are big,” Rosendale responds. “That’s what sent the NRA over the line. Because in ’12, with [Republican Senate nominee Denny Rehberg] they stayed out, they stayed out of Montana. But Chris Cox told me, he’s like, ‘We’re going to be in this race.’”

Sure enough, earlier this month, the NRA shelled out more than $400,000 on airtime for ads criticizing Tester for his votes on Trump’s Supreme Court nominations.

Some campaign finance watchdog groups told the Daily Beast the recording raises serious concerns about whether Rosendale was illegally coordinating with the NRA, a 501(c)(4) group that is not supposed to consult candidates on its spending in their races.

Rosendale’s comments about his conversation with the NRA’s Cox call into question whether the NRA and the Senate candidate fulfilled the Federal Election Commission’s “three-pronged” criteria for a violation, the Campaign Legal Center’s Brendan Fischer told the Daily Beast.

“The payment prong is satisfied because the ads were paid for by somebody other than Rosendale; the content prong is satisfied because the ads expressly advocate against the election of Rosendale’s opponent; and the conduct prong can be satisfied by Rosendale assenting to the request or suggestion of the entity paying for the ad: the NRA,” Fischer told the Daily Beast.

But it is unclear from the recording whether Rosendale assented to the suggestion of an ad buy or if he was merely told about it. Ultimately, that’s what the FEC would examine in this case.

Rosendale spokesman Shane Scanlon argued that it's the latter, that Rosendale was merely talking about securing the NRA's endorsement after it stayed on the sidelines of the 2012 race between Tester and Rehberg.

"The only thing this audio proves is that Matt sought the endorsement of the NRA — and we're proud to have it," Scanlon said in a statement. "Matt and the NRA have never discussed anything beyond the organization's membership and endorsement process."

"If Jon Tester is so desperate to save his seat, perhaps he should focus more on fighting for Montana and defending our Second Amendment rights rather than spreading lies about our campaign," Scanlon added.

Chris Meagher, the communications director for Tester’s campaign, said this isn’t the first time Rosendale has received scrutiny for shady campaign finance tactics, alluding to another Daily Beast report in July outlining how some donors used an accounting loophole to give more than the $5,400 maximum to his campaign.

“This audio raises serious concerns about potential illegal coordination between Matt Rosendale and an outside, dark money group coming into Montana to support him,” Meagher said in a statement Thursday. “At a minimum, this is just the latest in a troubling pattern of Matt Rosendale playing fast and loose with campaign finance laws.”

Rosendale and Tester are locked in what experts expect will be one of the closest Senate races of the midterms this November.

President Donald Trump won the state by 21 points in 2016, although Tester is known in the state as a hard campaigner.